: The goal of this project is to advance our understanding of the development of visual pattern sensitivity in human infants. Numerous and complex cues are available to judge spatial position in visual pattern elements; these cues include orientation, luminance contrast, temporal frequency, and spatial frequency. The proposed experiments are designed to determine the relative contributions of mechanisms sensitive to these different sources of information to infants' position sensitivity. The experiments will use an improved version of an established visual evoked potential (VEP) technique, and the most widely used test of position sensitivity, vernier acuity. The project will address the following questions: (1) What are the roles of spatiotemporal mechanisms in vernier acuity development? (2) Are vernier and grating acuity limited by different mechanisms? (3) What are the roles of orientation-sensitive filters in vernier acuity during development? Each experiment will measure different aspects of infants' VEP vernier responses during development, and compare these to adults' responses to determine the nature of the vernier response immaturity. Beyond analyzing the mechanisms of infant vernier acuity, the project will have potential value for clinical diagnosis. Vernier acuity is a more sensitive indicator than grating acuity of vision loss due to ambylopia. Specifically, vernier acuity is significantly more reliable than grating acuity in Snellen (letter chart) acuity in adult amblyopes. Vernier acuity is also selectively damaged in infants and children with cortical visual impairment. The proposed experiments on vernier acuity development will provide substantial normative data for designing new vision tests for infants at risk for amblyopia or cortical visual impairment.